The present invention generally relates to electric lamps and methods of manufacture. More specifically, the present invention relates to lamps having a gas filled outer lamp jacket.
In the manufacture of electric lamps, it is often desirable to provide a controlled atmosphere for many of the components of the lamp to prevent premature failure of the components and thereby prolong the operating life of the lamp. For example, the exposure of the filament of an incandescent lamp or the arc tube of an HID lamp to even very small amounts of oxygen during lamp operation will significantly degrade the components leading to lamp failure; thus shortening the operating life of the lamp. To prevent the exposure of such components to damaging atmospheres, it is well known to provide a controlled atmosphere for the components by enveloping the components in the desired atmosphere contained within an outer lamp jacket.
Many lamps are constructed having a lamp stem mounted at an open end of the outer lamp jacket. The typical lamp stem is formed from a glass tube having one or more electrical leads sealed at a pinched end of the tube and an exhaust tube forming a fluid passage through the stem. When the stem is mounted at the base of the outer lamp jacket, the exhaust tube provides the only fluid communication between the interior and the exterior of the outer lamp jacket. Once the outer lamp jacket has been evacuated and then filled with the desired fill gas, the stem exhaust tube is sealed to thereby hermetically seal the outer lamp jacket.
In lamps constructed with a stem, the known methods of controlling the atmosphere within the outer lamp jacket include the steps of evacuating the ambient atmosphere from the outer lamp jacket through the stem exhaust tube, and then either maintaining a vacuum or back-filling the jacket with a controlled atmosphere such as an inert gas. The known methods for evacuating the jacket through the stem exhaust tube include systems having one or more exhaust pumps and oil lubricated rotary valves to mechanically pump the ambient atmosphere from the interior of the jacket. Such methods suffer from several disadvantages. The pumps and valves are costly and require time consuming and costly maintenance to operate. Further, oil from the rotary valves may become atomized and then carried into the outer jacket during the flush or fill process. The presence of oil is known to be detrimental to the operation of many types of lamps. For example, the presence of oil may cause sodium loss in metal halide lamps and may lead to lamp failure.
It is often desirable to provide lamps wherein the pressure of the fill gas within the outer lamp jacket is other than atmospheric pressure at substantially room temperature. For example, many HID lamps include subatmospheric fill gas within the outer jacket to improve the containment of debris in the event of a failure of the arc tube mounted within the jacket. In the manufacture of lamps having stems, the vacuum pump system used to flush and fill the outer jacket is also used to control the final pressure of the fill gas. Thus the known methods of controlling fill gas pressure also suffer from the same disadvantages resulting from the use of the vacuum pump system to exhaust the outer jacket.
Accordingly, it is an object of the present invention to obviate many of the deficiencies of the prior art and provide a novel method of manufacturing electric lamps having gas filled outer lamp jackets.
It is another object of the present invention to provide a novel method of making lamps which obviates the need to use a vacuum pump system.
It is a further object of the present invention to provide a novel method of flushing and filling the outer lamp jacket of a lamp having a stem by discharging the fill gas into the interior of the outer jacket.
It is a further object of the present invention to provide a novel method of making lamps in which the interior of the outer lamp jacket remains open to an uncontrolled atmosphere during the step of sealing the stem exhaust tube.
It is yet another object of the present invention to provide a novel method of making lamps in which communication of an inert outer jacket fill gas with an uncontrolled atmosphere such as air is maintained until the outer jacket is hermetically sealed.
It is yet a further object of the present invention to provide a novel method of making lamps which obviates the need to use a vacuum pump system to control the final pressure of the fill gas contained within the outer lamp jacket.
It is still another object of the present invention to provide a novel method of making lamps in which the temperature of the fill gas contained within the outer lamp jacket is controlled until the jacket is sealed.
It is yet another object of the present invention to provide a novel method of making lamps having subatmospheric fill pressure within the outer lamp jacket in which there is no pressure differential at the time of sealing the jacket.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.